Parvovirus Infection in Dogs
Parvovirus is a highly contagious and deadly virus that can strike unvaccinated puppies and dogs. It primarily causes gastrointestinal disease, but secondary infection can affect other organs. The virus, which attacks and destroys the rapidly growing cells of the intestine, are transmitted by contaminated feces. Parvo virus is resiliant and able to exist in the environment for a long time. Parvo virus can be transmitted on objects such as grass, shoes, clothing, and other materials that touch infected surfaces.
The original canine parvovirus underwent several genetic alterations, developing into Parvo-1 and Parvo-2; Parvo-2 further mutated into a, b and c types. The most severe disease is associated with Parvo-2b which can also affect cats. Parvo-1 may cause unmanageable and usually fatal diarrhea in newborn puppies.
The highest risk of exposure is in breeding kennels, parks, animal shelters, and areas with a high number of puppies without adequate vaccination protection. Doberman pinschers, Pit bulls, Labrador retrievers, German shepherd dogs, English springer spaniels and Alaskan sled dogs are considered to be more susceptible to canine parvovirus infection than other breeds of dog.
The Signs of Illness
The primary signs are gastrointestinal and include loss of appetite, vomiting, lethargy, and diarrhea. Vomiting is often severe, and diarrhea may be profuse and bloody. Fever may be present, and animals can quickly become severely dehydrated. Affected dogs are often very weak, and shock may develop in some dogs from the dramatic loss of body fluids.
Most cases are seen between 6 weeks and 6 months of age with more severe disease seen in younger puppies. The incidence has decreased dramatically with vaccination of puppies against parvovirus.
Because parvovirus may cause infected dogs to become seriously ill, a number of tests may be done to assess the presence of the virus:
• A complete blood count may show low numbers of white blood cells, red cells (anemia) and platelets (needed for blood clotting).
There are quick and accurate snap tests that can be done on fecal samples in the veterinary clinic. However, false-positive tests are possible immediately after parvovirus vaccination , because non-infective virus is shed in the stool. False-negative tests are also possible, but rare.
There is no magic cure and the treatment of CPV is largely supportive, with intravenous fluids, sometimes plasma transfusions, anti-vomiting medications, and sometimes medications to protect the stomach. If anemia is severe, blood transfusions may be administered. Antibiotics may be given to control secondary bacterial infections. Severely ill dogs may develop a widespread bacterial infection (sepsis) because the protective barrier of the intestine is damaged. When sepsis occurs, it can adversely affect many other organs and usually requires intensive therapy.
Food and water are commonly withheld until no vomiting has occurred for 12-24 hours. Then small amounts of water or ice chips may be offered, and if that is tolerated well, bland food is reintroduced very slowly. Small portions are fed every 2-4 hours initially, after which the amount of food is gradually increased and the time between feedings is gradually lengthened. If the puppy recovers, recovery is typically complete; immunity following canine parvovirus infection is long term and may be lifelong.
Mortality is primarily due to the presence of bacterial toxins in the blood and widespread organ failure. Aggressive therapy improves survival, but mortality rates may still approach 30%. The cost of treatment can be expensive.
For known contaminated areas, the virus can be inactivated by sodium hypochlorite (a 1:20 dilution of common household bleach) after 10 minutes of contact time. All dirty material must be removed first, so that the bleach can reach the virus.
Vaccination against canine parvovirus drastically reduces the disease incidence. Modified live vaccines are recommended for puppies to minimize interference from maternal antibodies. Interference from maternal antibodies or weak immunity are the main reasons for vaccine failure in puppies.
Protocols recommend vaccinating against parvo at 6, 9, and 12 weeks of age. High-risk breeds may require a longer initial vaccination protocol against canine parvovirus, extending up to 22 weeks of age. According to the American Animal Hospital Association, revaccination should occur one year after the initial series and be revaccinated every 3 years thereafter.
About the Author: Dr. Mark Thompson, DVM graduated from The Ontario Veterinary College in 1977. He practiced small animal medicine in Ontario Canada before becoming a Technical Services Veterinarian for a company making medical diets for pets. Dr. Thompson has delivered hundreds of scientific presentations to veterinarians, technicians and pet owners across North America. Prior to joining Found Animals, he worked for the largest pet retailer in North America. He is currently working on opening Adopt & Shop stores in Southern California in order to find homes for adoptable shelter pets.
Sign-up for our pet club newsletters for information on pet care and more.